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Introduction:In refractory out-of-hospital cardiac arrest (OHCA), prolonged whole-body ischemia with global tissue injury proceeds even after achievement of reperfusion with extracorporeal cardiopulmonary resuscitation (eCPR).Hypothesis:Biomarkers reflecting ischemia and inflammation may be used for prognostication of refractory OHCA managed with eCPR.Methods:This nationwide retrospective study included patients (≥18 years) with refractory OHCA managed with eCPR in Denmark (2011 to 2020). Biomarker levels at admission, at 24 hours (lactate, leukocytes, and platelets), and repeated measures of lactate after eCPR initiation were analyzed. Lactate clearance was calculated as (admission lactate - post eCPR lactate) / admission lactate x100%.Results:Two hundred eighteen patients (80% male; age 52±12yrs) were included. Primary cause of OHCA was acute myocardial infarction (63%), 69% had shockable primary rhythm and 86% witnessed OHCA with a median low-flow time of 105 minutes (Q1-Q3: 86-124 min.). Fifty-three (24%) survived to hospital discharge. Survivors had a significantly lower lactate level at admission (13.1 vs. 15.4 mmol/l, p=0.004) and after 24 hours (2.8 vs. 5.0, p=0.001), and a significantly higher admission platelet level (181 vs. 153 x109/l, p=0.03). No difference in admission levels of leukocytes nor leukocytes and platelets after 24 hours were found between survivors and non-survivors. Lactate clearance was available for 68% and 79% of patients alive after 8 and 24 hours, respectively. All survivors had a lactate level less than admission lactate at 8 hours (lactate clearance >0%) and had cleared >25% of admission lactate at 24 hours after eCPR initiation. There was a significant difference in survival between quartiles of lactate clearance at 8 hours after eCPR initiation (Figure 1).Conclusion:In conclusion, early lactate clearance after eCPR initiation was associated with survival to discharge in refractory OHCA-patients.